Ethernet Overview

Last modified by Microchip on 2023/11/09 08:54

Ethernet is a Data Link and Physical Layer protocol defined by the IEEE 802.3™ Specification. It comes in many flavors, defined by maximum bit rate, mode of transmission, and physical transmission medium:

  • Maximum Bit Rate (Mbits/s): 10, 100, 1000, etc.
  • Mode of Transmission: Broadband, Baseband.
  • Physical Transmission Medium: Coax, Fiber, UTP, etc.

OSI Model Basics

One of the things that have made Ethernet so widely adopted is the Open Systems Interconnection (OSI) model. OSI is a model of the many layers involved when two intelligent devices share information. With this model, you, as the developer of the Application Layer, do not need to know about the physical medium that data is being transmitted on, you can just focus on presenting the data. The OSI model has seven layers, but TCP/IP reduces these to five.

Here, the OSI model is mapped to the Internet Engineering Task Force Transmission Control Protocol/Internet Protocol (TCP/IP) (Software) and Ethernet (Hardware) realities.

The "Medium" is not considered part of the OSI model, however, it falls within the IEEE 802 specification and forms the basis for naming all of the Ethernet Families.

OSI model

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Ethernet Families

The Ethernet physical layer has evolved over time to utilize several media interfaces and transmission speeds.

Physical Media


Twisted Pair

1 Mbps
10 Mbps
100 Mbps
1000 Mbps
10 Gbps
100 Gbps

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Ethernet Family Naming Scheme

Ethernet families are named according to certain medium specifications:

Ethernet naming scheme

For example, Fast Ethernet is named:

Fast ethernet name

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Bit Rate

The nominal usable speed for the MAC layer.


  • 10, 100, 1000 (no suffix = megabits/second)
  • 10G (G suffix = gigabits/second)

Signaling Type

  • BASE - Baseband signaling (most common type)
  • BROAD - Broadband signaling
  • PASS - Passband signaling


PCS Encoding

Certain bit encoding schemes are employed at certain speeds to reduce the required transmission bandwidth.

  • X = 8b/10b block encoding (Gigabit ethernet) or 4b/5b (Fast Ethernet)
  • R = 64b/66b for large blocks (10G ethernet)


Refers to the number of signal-carrying wires (or wire pairs) used per link (1, 2, 4, 10).

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Common Families Supported by Microchip

Family TypeMediumData RateSegment Length
10BASE-TUTP (Unshielded twisted pair)10 Mbps100 m
100BASE-TX2-Pair CAT5 UTP100 Mbps100 m
100BASE-FX2 Optical Fibers100 Mbps100 m
1000BASE-T4-Pair CAT5 UTP1000 Mbps100 m

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